112 



COALFIELDS AND COLLIERIES OK AUSTRALIA. 



There are three classes of weighing machines at this mine 

 Pooley's weighing machine, with a turn-table; a steelyard; 

 and a Billy fair-play. The last is not now in use. It consisted 

 of a large Salter's spring balance, connected by rods to a box 

 made large enough to hold the slack from one skip. The bot- 

 tom of the box is on an axle, which is placed a little on one 

 side of the centre, so that it can be easily tipped up by means 

 of a lever attached to the axle. TV>e slack that falls through 

 the screen collects in this box, and the weight can be read on 

 the face of the dial of the spring balance. The bottom is then 

 turned up, and the contents emptied into a railway truck. 



Fig. 50. Screens and Waggons. 



Hopper waggons are used for shipping coal, so that the bodies 

 can be readily lifted out by cranes. But the D class of 

 waggon is used for local consumption. To keep lump coul 

 from sliding down the screens too quickly, and carrying slack 

 with it, a series of so-called knives are placed between the 

 bars, and, sticking up, retard the rush of coal (Fig. 50). These 

 knives have their other ends weighted, and, when the pressure 

 becomes too great, the knives are forced down so that the coal 

 can get past; but the weight enables the knives to assume 

 their erect position as soon as the pressure is relieved. The 



